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People with certain personality disorders (mainly borderline, narcissistic, compulsive-obsessive, schizotypal, and paranoid) have a "persecutory object". It is a tormenting, devaluing, and sadistic inner voice (introject). It repeatedly and authoritatively informs them that they are bad, worthless, weak, immoral, and a disappointment.
Such an inner critic, a relentless integrated prosecutor and judge is of course intolerable. In an attempt to exorcise it, the patient projects it - usually onto an intimate partner. The spouse, mate, or lover then become the outer embodiment or reification of the internal agonizing construct.
The persecutory object also serves as an organizing and explanatory principle. The patient’s inner processes and life events are accounted for by attributing them to the nefarious presence, intentions, and actions of the malicious intimate partner. Even the patient’s attachment to her spouse is interpreted as the lamentable outcome of brainwashing and manipulation. Everything that goes wrong in the patient’s tortured existence is her partner’s fault, an almost supernatural emanation from his malevolence or, at the very least, indifference and rejection.
The patient tries to coerce and shoehorn the intimate partner into behaving in a way that upholds his newfound status as an enemy and a threat. This defense mechanism is known as "projective identification". If the intimate partner has his own issues, he will comply in his assigned role and transform himself into an abuser ("introjective identification"). The patient then proceeds to rebel against her externalized persecutory object (=her intimate partner), punish, and defy him by behaving promiscuously and cheating ("being a slut or whore"); envying and sabotaging her partner's career; passive-aggressively challenging and provoking him; humiliating, rejecting, and undermining his well-being and self-esteem; compromising his public image and standing in society; and penalizing him in myriad other ways.
Naturally, the patient then expects a penalty commensurate with her egregious misbehavior. She becomes paranoid, hypervigilant, and exceedingly anxious. These dissonant emotions only augment her perception of the intimate partner as a source of unmitigated sadistic control and judgment, an imminent and omnipresent threat, and the fount of ambivalence (love-hate relationship).
(From the book "Malignant Self-love: Narcissism Revisited" by Sam Vaknin - Click on this link to purchase the print book, or 16 e-books, or 3 DVDs with 16 hours of video lectures on narcissists, psychopaths, and abuse in relationships: http://www.narcissistic-abuse.com/thebook.html)